Ultra-large scale integrated circuits (ULSI), microelectronics, optoelectronics, and other electronic devices and products generally require fine interconnection or conductive patterns to accommodate functionality and density constraints. However, fine interconnection patterns are increasingly difficult to control. For example, one material used to form interconnection patterns is copper. Copper may be used for interconnection patterns rather than aluminum materials because copper generally has a higher conductivity, substantially no hillocks formation, and substantially no electron migration. Actually, copper interconnection may be required for the sub 180 nanometer ULSI. However, one problem associated with copper trace or line formation is that there is a lack of an effective dry etching process to prepare well-controlled copper fine lines. For example, copper lines are generally prepared with a chemical mechanical polishing (CMP) process, such as Damascene or dual-Damascene. However, when the minimum device geometry is reduced or shrunk to less than 100 nanometers, such a process is especially difficult for use in etching and filling high aspect ratio structures.
Plasma etching of copper has also been used to form interconnection patterns. For example, the most common etching chemistry is derived from an aluminum etch, i.e., using halogen-containing gases as the feed streams. Since the reaction products of the plasma etch, i.e., copper halides, have very low volatilities at room temperature, the reaction products often accumulate on the surface of the product or device instead of being removed. In order to facilitate the removal of these halides, a high-energy source, such as a high-density plasma, a laser, an infrared (IR) or ultraviolet (UV) beam, or a high substrate temperature, needs to be added to a reactive ion etching (RIE) chamber. Such methods either may have poor etch uniformity for large area substrates or require a complicated reactor design and process control scheme. The high temperature approach does not have the above described problems, but still requires high ion bombardment energy to achieve a high etch rate. Additionally, the selectivity of copper or other interconnection materials to another film will generally be lowered by the high ion bombardment energy. In many of the copper etching processes, for example, the etch rate is negative, i.e., the etched surface is higher than the unetched surface due to the accumulation of the reaction product.